Proceedings of The Physiological Society

University of Oxford (2011) Proc Physiol Soc 23, PC46

Poster Communications

Functional and molecular defects of baroreceptor neurons in genetic hypertension

Y. Lu1, V. Snitsarev1, C. A. Whiteis1, M. W. Chapleau1,2, F. M. Abboud1

1. Internal Medicine & Cardiovascular Center, University of Iowa, Iowa City, Iowa, United States. 2. Veterans Affairs Medical Center, Iowa City, Iowa, United States.

We have reported that important determinants of baroreceptor nerve activity include the mechanosensitive Acid Sensing Ion Channel-ASIC2 (Neuron 2009), the calcium-activated K+ channel-BK (J Physiol 2007) and Na+K+ATPase (Am J Physiol 1984). Our goal was to test the hypothesis that genetic dysregulation of these and other ionic events in baroreceptor neurons account for the impaired baroreceptor nerve activity in the spontaneously hypertensive rat (SHR). We injected the red fluorescent dye (DiI) into the wall of the aortic arch of anesthetized (Ketamine/Xylazine 91/12.5 mgm/kg I.P.) SHR and Wistar Kyoto (WKY) control rats. The arch contains the sensory terminals of aortic baroreceptor neurons which reside in the nodose ganglia. Ten days later the ganglia were surgically removed from the deeply anesthetized rats (1cc isoflurane in 1,000cc air) and their cells were dispersed in culture to identify the labeled baroreceptor neurons. Electrophysiologic responses to mechanical stimulation (puffing of saline at 10 psi from a pico-pump) and to depolarizing current injections (1-10nA) were obtained with sharp microelectrodes. SHR neurons had a more negative resting membrane potential (RMP) than those from WKY (-61.3±2.7, n=17 vs. -43.9±1.9 mV, n=24*); were not depolarized by mechanical stimulation (Δ-2.3±1.0 mV, n=15 vs. Δ+6.8±2.4 mV, n=20*), and did not fire action potentials during 1nA current injections (0.5±0.3, n=16 vs. 5.8±2.7 spikes/s, n=22*) or during their impalement with the microelectrode (0.5±0.1, n=18 vs. 179±63 spikes, n=19*) (*p=<0.01). PCR arrays of nodose ganglia showed that only 2 genes (Atp1b1 and Atp1b2) were upregulated in SHR vs. WKY by 3.0 and 9.3 fold respectively. These genes encode Na+K+ATPase alpha and beta polypeptides. Among the downregulated genes in SHR, Accn1 (ASIC2) was reduced by 3.1 fold; kcnmb1 (BK beta1) by 3.7 fold; and several voltage-gated K+ channels (e.g. Kcna1 / Kv1.1; Kcna4 / Kv1.4; Kcnj4 / Kir2.3; Kcnd2 / Kv4.1-A current) by -1.9, -2.7, -6.7, -2.5 fold respectively. mRNA (qRT-PCR) and proteins confirmed the directional changes in gene expression seen in PCR arrays in SHR. microRNAs which are putative inhibitors of the genes mentioned accounted for some of the changes in gene expression. Ten miRNAs were upregulated and nine were downregulated more than 4 fold. Of these, the upregulated miR34c correlates with decreased ASIC2 and the downregulated miR-29a, miR-29c, miR-142-3p, miR-181a-1, miR-181c, miR-363 may explain the overexpression of Na+K+ATPase. The results suggest that the molecular profile of enhanced Na+K+ATPase and reduced ASIC2, BKbeta1 and Kv may explain the more negative RMP, and decreased mechanosensitivity and excitability of SHR neurons. Thus we have identified molecules responsible for defective sensory signaling of baroreceptor neurons in SHR. Therapies targeting these molecules may restore baroreflex sensitivity and reduce blood pressure and mortality in hypertension.

Where applicable, experiments conform with Society ethical requirements